1. Field of the Invention
The present invention relates to an illumination control apparatus having a DRL automatic lighting function that automatically lights an illuminating lamp at power (lower light quantity) lower than that in normal lighting in a vehicle when a DRL executing condition is held.
2. Description of the Related Art
In vehicles of four-wheel cars, there is a model which is equipped with a function of automatically executing an operation called DRL (Daytime Running Lights) that lights illuminating lamps (for example, headlight lamps) for safe drive in daytime (in this specification, it is called a DRL automatic lighting function as the case may be). The DRL automatic lighting function is to automatically light illuminating lamps when a predetermined DRL executing condition is held (for example, an ignition switch is on, a parking brake is off, and a user does not effect any manual lighting operations for illumination). In the DRL automatic lighting function, generally for securing safety against an oncoming car and for energy saving, lamps are lit in light quantity lower than the manual lighting state by a user's manipulation (typically, the lighting state in running at night) as voltage applied to the lamps is lowered. Therefore, when the DRL automatic lighting function is operated, the lamps are PWM-driven by using a switching device such as an FET, for example. For an illumination control apparatus for controlling the lamps, an apparatus having the DRL drive function for lamps like this is equipped.
Patent Reference 1 describes an automobile head lamp control circuit having the DRL automatic lighting function described above. The circuit implements the DRL automatic lighting function by PWM-driving high beam lamps under control by a microcomputer when a DRL executing condition is held.
Patent References 2 and 3 disclose techniques relating to detecting a break in a lamp in vehicles.
Patent Reference 1 JP-A-10-86746
Patent Reference 2 JP-A-4-342632
Patent Reference 3 JP-UM-A-4-60732